I. Field of the Invention
This invention relates to improvements in a process for the conversion of methanol to hydrocarbons, to improvements in a Fischer-Tropsch process, and to improvements in Fischer-Tropsch catalysts. In particular, it relates to improved cobalt catalysts, and process for using such catalysts in the conversion of methanol, and Fischer-Tropsch synthesis to produce hydrocarbons, especially Cl.sub.10 + distillate fuels, and other valuable products.
II. The Prior Art
Methane is often available in large quantities from process streams either as an undesirable by-product in admixture with other gases, or as an off gas component of a process unit, or units. More importantly, however, methane is the principle component of natural gas, and it is produced in considerable quantities in oil and gas fields. The existence of large methane, natural gas reserves coupled with the need to produce premium grade transportation fuels, particularly middle distillate fuels, creates a large incentive for the development of a new gas-to-liquids process. Conventional technology, however, is not entirely adequate for such purpose. Nonetheless, technology is available for the conversion of natural gas, to produce methanol, a product of currently limited market ability. However, to utilize the existing technology, there is a need for a process suitable for the conversion of methanol to high quality transportation fuels, particularly middle distillate fuels. On the other hand, the technology to convert natural gas, or methane, to synthesis gas is well established, and the conversion of the synthesis gas to hydrocarbons can be carried out via Fischer-Tropsch synthesis.
Fischer-Tropsch synthesis for the production of hydrocarbons from carbon monoxide and hydrogen is now well known in the technical and patent literature. The first commercial Fischer-Tropsch operation utilized a cobalt catalyst, though later more active iron catalysts were also commercialized. An important advance in Fischer-Tropsch catalysts occurred with the use of nickel-thoria on kieselguhr in the early thirties. This catalyst was followed within a year by the corresponding cobalt catalyst, 100 Co:18 ThO.sub.2 :100 kieselguhr, parts by weight, and over the next few years by catalysts constituted to 100 Co:18 ThO.sub.2:200 kieselguhr and 100 Co:5 ThO.sub.2:8 MgO:200 kieselguhr, respectively. The Group VIII non-noble metals, iron, cobalt, and nickel have been widely used in Fischer-Tropsch reactions, and these metals have been promoted with various other metals, and supported in various ways on various substrates. Most commercial experience has been based on cobalt and iron catalysts. The cobalt catalysts, however, are of generally low activity necessitating a multiple staged process, as well as low synthesis gas throughput. The iron catalysts, on the other hand, are not really suitable for natural gas conversion due to the high degree of water gas shift activity possessed by iron catalysts. Thus, more of the synthesis gas is converted to carbon dioxide in accordance with the equation: H.sub.2 +2CO.fwdarw.(CH.sub.2).sub.x +CO.sub.2 ; with too little of the synthesis gas being converted to hydrocarbons and water as in the more desirable reaction, represented by the equation: 2H.sub.2 +CO.fwdarw.(CH.sub.2).sub.x +H.sub.2 O.
There exists a need in the art for a process useful for the conversion of methanol and synthesis gas at high conversion levels, and at high yields to premium grade transportation fuels, especially C10+ distillate fuels; particularly without the production of excessive amounts of carbon dioxide.